Dear Christopher Cat

I got cat scratch disease this fall. My cat was never sick, so how did she give me this disease?

Christopher Responds

Cat scratch disease is caused by bacteria known as Bartonella henselae that live in the guts of infected fleas. These bacteria are present in flea excrement, called flea dirt, which the flea deposits on your cat’s hair coat.

The bacteria are thought to be introduced into a person’s skin by a cat scratch that becomes contaminated with flea dirt. The person then develops cat scratch disease, which usually starts with tender, swollen lymph nodes near the scratch.

Cats can become infected by the bacteria through flea bites, but they generally don’t show obvious clinical signs. Blood tests are not always accurate because bacteria levels in the cat’s blood wax and wane for a few years until the cat’s immune system overcomes the bacteria.

Antibiotics are not effective in eliminating the bacteria in cats. People sometimes are scratched when they pill their cats, so it’s just not practical to medicate cats suspected of carrying the disease.

The best way to prevent cat scratch disease is to keep your cat flea-free and trim her claws periodically.

To check for fleas, comb her with a fine-tooth comb such as a flea comb. If your comb collects any tiny black specks (flea dirt), smear them onto a wet paper towel. Because flea dirt is digested blood, the smear will produce red-brown streaks.